Ancient Lineages of the Western and Central Palearctic: Mapping Indicates High Endemism in Mediterranean and Arid Regions

Abstract

The Palearctic region is characterised by high endemism in the west and east, and a low endemism centre. The endemic lineages occurring at the two ends are largely distinct, and eastern endemics are typically associated with humid climates and forests, representing the start of a continuum from temperate to tropical forest groups and leading to Indo-Malay endemics. In contrast, western Palearctic endemics are typically associated with arid or seasonally dry (Mediterranean) climates and vegetation. Those lineages occurring in the central Palearctic are typically of western origin. Here, we use phylogenetic age (older than 34 million years (My)) to define a list of tetrapod and vascular plant lineages endemic to the western and central Palearctic, map their distributions at the ecoregion scale, and combine these maps to illustrate and understand lineage richness and endemism patterns. Sixty-three ancient lineages were recovered, approximately half of them reptiles, with several herbaceous and shrubby angiosperms, amphibians, and rodents, and single lineages of woody conifers, insectivores, and birds. Overall, we show high lineage richness in the western Mediterranean, eastern Mediterranean, and Iran, with the highest endemism values recorded in the western Mediterranean (southern Iberian Peninsula, southern France). This paints a picture of ancient lineage survival in areas of consistently dry climate since the Eocene, but also in association with persistent water availability (amphibians in the western Mediterranean). The almost complete absence of ancient endemic bird lineages is unusual and perhaps unique among the world’s biogeographic regions. The factors accounting for these patterns include climate since the end of the Eocene, micro-habitats and micro-climates (of mountain terrain), refugia, and patchiness and isolation (of forests). Despite their aridity adaptations, some of the lineages listed here may be tested under anthropogenic climatic change, although some may extend into the eastern Palearctic. We recommend using these lineages as flagships for conservation in the study region, where their uniqueness and antiquity deserve greater recognition.

1. Introduction

The Palearctic is a well-established region [1], acknowledged in most global regionalisation studies [2,3,4], with mostly minor differences in delimitation. The western part of the region (Europe, in particular, but also the Mediterranean Basin and Middle East) is where systematic biodiversity exploration started. A more recent focus on the hyper-diverse tropics has somewhat overshadowed the importance of regions like the Palearctic, given its lower species richness and endemism for such a vast area of the globe.

Nevertheless, recent mapping of ancient lineages [5] shows that the western Palearctic is, in fact, very interesting by hosting quite a few of these lineages, some range-restricted ones of Jurassic age. The same study shows that the eastern Palearctic is globally extraordinary in terms of the number of ancient endemic lineages, on the one hand, representing a transition zone towards the Indo-Malay Region, which is arguably the world’s richest region when it comes to ancient lineages [6], and, on the other, having its own unique lineages, mostly forest dwellers and, as such, requiring a humid climate. Even though this section, especially the Sino-Himalayan subregion (e.g., [3]), if included in the Palearctic, only represents a small fraction of its surface area, more than half of all Palearctic biodiversity is only found here. Thus, a study on the Palearctic including endemics for this section would likely end up focussing on the lineages endemic to East Asia.

The comparatively species-poor and endemic-poor central Palearctic appears more similar to the west, with most lineages that live there being cold- and aridity-adapted [7]. Typically, the Palearctic is taken to include the temperate and arid parts of Eurasia and North Africa (e.g., [3]), although, more recently, the tropical arid section of North Africa and Asia is sometimes treated as a separate region [2,4,8]. Biogeographical studies within the Palearctic as a whole have been sparse [9,10], with studies focussing on specific lineages (or taxonomic groups) within parts of the broader region or, more specifically, the western Palearctic (e.g., [11,12]).

Here, we focus on endemic or near-endemic ancient tetrapod and plant lineages (greater than 34 My (million years) old). We consider patterns in the richness and endemism of these ancient lineages at the ecoregion scale in order to better understand the place of the Palearctic in global biogeography.

2. Materials and Methods

The endemism-defined study area includes all of Europe, North Africa down to the Sahel and including Macaronesia, the Middle East, including arid ecoregions to the Thar Desert, Central Asia, western China, Tibet (including temperate but not tropical ecoregions in the Himalayas), and most of Siberia, with the exception of Kamchatka, Magadan, and the Ussuri. The most difficult delimitation was in the Chinese provinces of Yunnan and Sichuan. Here, the biodiverse forest ecoregions were viewed as part of the eastern Palearctic and, thus, excluded, whereas grassland ecoregions were regarded as extensions of the Tibetan Plateau and, therefore, included. A lineage was considered endemic if ≥80% of the ecoregions where it occurs fell within the study area. This means that, when mapping near-endemic lineages, some of them extend into the eastern Palearctic and Indo-Malay regions, and, in some cases, even into the eastern part of the Afrotropical region (the arid ecoregions in the Horn of Africa southwards as far as Kenya (where many Middle Eastern lineages extend to)).

We listed and mapped tetrapod and plant endemic ancient lineage diversity using the cut-off age of 34 My, as in Padayachee and Procheş [13], these two groups being relatively well studied taxonomically, distributionally, and phylogenetically. The dates for lineage divergence were derived primarily from three sources: Rosindell and Harmon [14] (tetrapods and plants, globally), Roquet et al. [15] (tetrapods only, for Europe and surrounding regions, but not covering the entire study area), and Garcia-Porta et al. [16] (family Lacertidae only, globally).

Mapping was performed at the ecoregion level [17]. Methods largely followed Procheş et al. [5], using ecoregions and data for animal lineages from the WildFinder database [18], while plant lineage data were obtained from the Angiosperm Phylogeny Website [19] and, additionally, from iNaturalist [20] and the Global Biodiversity Information Facility [21] data. Richness was calculated by summing up all the lineages present within an ecoregion and, subsequently, calculating weighted endemism (WE) (e.g., [22,23]). Maps were generated using ArcGIS Pro 3.4 [24].

3. Results

3.1. Lineage Coverage and Ages

In total, 63 lineages were found that are older than 34 My, of which 50 and 13 were tetrapod and plant lineages, respectively (

Table 1. Details of animal and plant lineages used in this study. Also included are lineage ages (eras or periods) with supporting references.

Genera Included	Family	Order	Age (Era/Period)	References
Salamandrella	Hynobiidae	Urodela	Cenozoic	[14,15]
Paradactylodon + Ranodon	Hynobiidae	Urodela	Cenozoic	[14,15]
Proteus	Proteidae	Urodela	Cretaceous	[14,15]
Chioglossa	Salamandridae	Urodela	Cenozoic	[14,15,25]
Salamandra + Lyciasalamandra	Salamandridae	Urodela	Cenozoic	[14,15,25]
Salamandrina	Salamandridae	Urodela	Cenozoic	[14,15,25]
Calotriton + Triturus + Lissotriton + Ommatotriton + Ichthyosaura + Neurergus	Salamandridae	Urodela	Cenozoic	[14,15,25]
Speleomantes	Pletodontidae	Urodela	Cenozoic	[14,15]
Alytes	Alytidae	Anura	Cretaceous	[14,15]
Discoglossus	Alytidae	Anura	Cretaceous	[14,15]
Pelobates	Pelobatidae	Anura	Cretaceous	[14,15]
Pelodytes	Pelodytidae	Anura	Jurassic	[14,15]
Desmana + Galemys	Talpidae	Eulipotyphla	Cenozoic	[14,15,26]
Muscardinus	Gliridae	Rodentia	Cenozoic	[14,15,26]
Selevinia + Myomimus	Gliridae	Rodentia	Cenozoic	[14,15,26]
Myoxus	Gliridae	Rodentia	Cenozoic	[14,15,26]
Allactaga	Dipodidae	Rodentia	Cenozoic	[14,15,26]
Allactodipus	Dipodidae	Rodentia	Cenozoic	[14,15,26]
Pygeretmus	Dipodidae	Rodentia	Cenozoic	[14,15,26]
Calomyscus	Calomyscidae	Rodentia	Cenozoic	[14,15,26]
Myospalax + Eospalax + Spalax + Nannospalax	Spalacidae	Rodentia	Cenozoic	[14,15,26]
Urocynchramus	Urocynchramidae	Passeriformes	Cenozoic	[14,15]
Natrix	Colubridae	Squamata	Cenozoic	[15]
Blanus	Blanidae	Squamata	Cenozoic	[15]
Euleptes	Sphaerodactylidae	Squamata	Cenozoic	[15]
Quedenfeldtia	Sphaerodactylidae	Squamata	Cenozoic	[15]
Saurodactylus	Sphaerodactylidae	Squamata	Cenozoic	[15]
Bunopus + Crossobamon	Gekkonidae	Squamata	Cenozoic	[15]
Tropiocolotes	Gekkonidae	Squamata	Cenozoic	[15]
Cyrtopodion + Carinatogecko	Gekkonidae	Squamata	Cenozoic	[15]
Agamura	Gekkonidae	Squamata	Cenozoic	[15]
Stenodactylus	Gekkonidae	Squamata	Cenozoic	[15]
Alsophylax	Gekkonidae	Squamata	Cenozoic	[15]
Ophiomorus	Scincidae	Squamata	Cretaceous	[15]
Ablepharus	Scincidae	Squamata	Cenozoic	[15]
Chalcides	Scincidae	Squamata	Cenozoic	[15]
Uromastyx + Saara	Agamidae	Squamata	Cenozoic	[15]
Phrynocephalus	Agamidae	Squamata	Cenozoic	[15]
Trapelus + Bufoniceps	Agamidae	Squamata	Cenozoic	[15]
Laudakia	Agamidae	Squamata	Cenozoic	[15]
Podarcis	Lacertidae	Squamata	Cenozoic	[15,16]
Zootoca + Archaeolacerta + Teira + Scelarcis	Lacertidae	Squamata	Cenozoic	[15,16]
Eremias	Lacertidae	Squamata	Cenozoic	[15,16]
Acanthodactylus	Lacertidae	Squamata	Cenozoic	[15,16]
Ophisops	Lacertidae	Squamata	Cenozoic	[15,16]
Mesalina	Lacertidae	Squamata	Cenozoic	[15,16]
Gallotia	Lacertidae	Squamata	Cenozoic	[15,16]
Psammodromus	Lacertidae	Squamata	Cenozoic	[15,16]
Atlantolacerta	Lacertidae	Squamata	Cenozoic	[15,16]
Omanosaura	Lacertidae	Squamata	Cenozoic	[15,16]
Cedrus	Pinaceae	Pinales	Jurassic–Cretaceous	[14,27,28]
Hypecoum	Papaveraceae	Ranunculales	Cretaceous	[14,27,29]
Leontice + Gymnospermium	Berberidaceae	Ranunculales	Cenozoic	[14,27]
Helleborus	Ranunculaceae	Ranunculales	Cenozoic	[14,27]
Nigella	Ranunculaceae	Ranunculales	Cenozoic	[14,27]
Aethionema + Moriera	Brassicaceae	Brassicales	Cenozoic–Cretaceous	[14,27,30]
Drosophyllum	Drosophyllaceae	Caryophyllales	Cenozoic	[14,27]
Cynomorium	Cynomoriaceae	Saxifragales	Cenozoic–Cretaceous	[19,27]
Biebersteinia	Biebersteiniaceae	Sapindales	Cretaceous	[14,27]
Tetradiclis	Nitrariaceae	Sapindales	Cenozoic	[14,27]
Cneorum	Rutaceae	Sapindales	Cenozoic	[14,27,31]
Ixolirion	Ixoliriaceae	Asparagales	Cenozoic–Cretaceous	[14,27,32]
Aphyllanthes	Asparagaceae	Asparagales	Cenozoic–Cretaceous	[14,27,32]

). Most lineages were equivalent to one genus each, but several included more than one genus (eleven animal lineages and two plant lineages; thirteen in total). In these cases, none of the single genera included would meet the age criterion used here in defining antiquity if taken separately, but multiple-genera monophyletic groupings did. A few of the single-genus lineages are recognised as distinct at the family level, and as such, the entire families are endemic to the study region (Pelobatidae, Pelodytidae, Calomyscidae, Urocychramidae, Drosophyllaceae, Cynomoriaceae, Biebersteiniaceae, Ixoliriaceae).

In the case of animals, there were 28 lineages for order Squamata, while the remaining lineages in descending ordinal rank were as follows: eight (Urodela), eight (Rodentia), four (Anura), and one each for Eulipotyphla and Passeriformes. All the lineages of the order Squamata have a Cenozoic origin, except Ophiomorus, which is older (Cretaceous). Lineages for the order Urodela have a Cenozoic origin, except for Proteus, which is from the Cretaceous. All lineages in the order Rodentia have a Cenozoic origin. Three of the four order Anura lineages are of Cretaceous origin, while Pelodytes dates back to the Jurassic. The single lineages from orders Eulipotyphla (Desmana + Galemys) and Passeriformes (Urocynchramus) are Cenozoic in origin (Table 1).

Most of the plant lineages were from the order Ranunculales (n = 4), followed by Sapindales (n = 3), Asparagales (n = 2), and one lineage each in the following orders: Pinales, Brassicales, Caryophyllales, and Saxifragales. Three of the four lineages from Ranunculales are Cenozoic in origin, while Hypecoum dates to the Cretaceous. The order Sapindales has two lineages that are Cenozoic in origin, with Biebersteinia from the Cretaceous. Both the lineages from Asparagales have Cenozoic–Cretaceous origins. The orders Pinales, Brassicales, and Saxifragales have a single lineage dating to the Cenozoic–Cretaceous, while Caryophyllales (also single-lineage) is Cenozoic in origin (Table 1).

3.2. Lineage Richness

Collectively, for all lineages, the richness is highest in the Mediterranean Basin from the Iberian Peninsula extending in a disjunct pattern into the Middle East (Figure 1a). The highest richness is found in three forested or partly forested ecoregions (n = 25 lineages): Eastern Mediterranean conifer–sclerophyllous–broadleaf forests, Northeastern Spain and Southern France Mediterranean forests, and Zagros Mountains forest steppe (see Supplementary Data Table S1 for details). High lineage richness (n = 21–23 lineages; six ecoregions) was also found in the partly forested ecoregions, mostly of the Mediterranean Basin (Aegean and Western Turkey sclerophyllous and mixed forests, Cantabrian mixed forests, Southwest Iberian Mediterranean sclerophyllous and mixed forests), one montane steppe ecoregion (Eastern Anatolian montane steppe), and also two desert ecoregions of the Middle East (Central Persian desert basins; Kopet Dag semi-desert). Richness declined latitudinally northwards (into the Arctic) and southwards (into North Africa), as well as longitudinally eastwards into Asia.

3.3. Lineage Endemism

Endemism is highest in the Mediterranean Basin, viz. Iberian Peninsula, Spain, and coastal France (Figure 1b). The highest values (WE = 5.0–6.0, two ecoregions) are in forested (Northeastern Spain and Southern France Mediterranean forests) and partly forested (Southwest Iberian Mediterranean sclerophyllous and mixed forests) ecoregions (Supplementary Data Table S1). High levels of endemism (WE = 4.0–4.9, seven ecoregions) are also found in six forested or partly forested ecoregions mostly in the Mediterranean Basin (Cantabrian mixed forests, Italian sclerophyllous and semi-deciduous forests, Iberian sclerophyllous and semi-deciduous forests, Zagros Mountains forest steppe, Eastern Mediterranean conifer–sclerophyllous–broadleaf forests, Mediterranean woodlands and forests). There is also one desert ecoregion in the Middle East with high endemism (Central Persian desert basins). Like richness, endemism gradually declined latitudinally northwards (into the Arctic) and southwards (into North Africa), as well as longitudinally into Asia.

Interestingly the following five forested or partly forested ecoregions from the Mediterranean Basin rank high for both richness and endemism: Eastern Mediterranean conifer–sclerophyllous–broadleaf forests, Northeastern Spain and Southern France Mediterranean forests, Zagros Mountains forest steppe, Cantabrian mixed forests, and Southwest Iberian Mediterranean sclerophyllous and mixed forests. Additionally, the Central Persian desert basins also rank high in richness and endemism. These results reaffirm the Mediterranean forests and associated transitional vegetation types as a stronghold for ancient Palearctic lineages.

4. Discussion

The Mediterranean Basin showed the highest ancient richness and endemism. It is a biodiversity hotspot with high levels of endemism and species richness. The diverse climatic zones, geomorphology, habitats, and vegetation have contributed to this richness and endemism of the basin [33]. Furthermore, the present study showed a general eastward decrease in ancient lineage diversity. This pattern has already been shown for amphibians [34]. The origin of the Central Asian steppe–desert in the early–middle Eocene has played a role in this trend. The Central Asian steppe–desert would have established at the end of the Eocene [7], the cut-off age of this study (34 My). During the Miocene, at least some landscapes in the Mediterranean Basin were modified by climatic changes (mainly cooling and aridification). Several palaeotropical taxa survived the environmental and climatic changes of the Miocene and Pliocene to form part of the modern flora of the Iberian Peninsula [35]. The ancient lineages of this study would have also been subjected to and survived these changes.

Our areas of highest richness and endemism are also characterised by mountainous terrain. Mountains, with diverse micro-climates and topographic complexity, are known to promote high richness, both due to high endemism and the accumulation of more widespread species [36]. A disproportionate level of taxonomic diversity occurs within topographically complex regions [37]. Steep gradients, soils, and micro-climates contribute to high endemism [38]. Mountainous regions that display topographical complexity and heterogeneity could maintain ancient lineages and account for the patterns observed. Molina-Venegas et al. [39] found that centres of plant palaeoendemism were clustered in the vicinity of the Strait of Gibraltar (Baetic–Rifan Range) (Southwest Iberian Mediterranean sclerophyllous and mixed forests ecoregion). Palaeoendemism was positively correlated with total annual precipitation, while endemic species richness showed a poor correlation. Elevation range showed a strong correlation with endemic species richness [39]. Topographical relief may have driven the diversification of newly evolved species. However, water availability was more critical for the long-term persistence of ancient lineages in refugia of smoother (presumably flatter) topography [39]. The richness, endemicity, and rarity of mammals could be due to refuge areas in the southern Mediterranean peninsulas [40], but most studies tend to focus on recent glacial refugia in the Mediterranean Basin [41]. Most of the Palearctic Pleistocene mammalian fauna retreated eastwards to the central Eurasian steppes rather than northwards to the Arctic Region. The central Eurasian Altai and Sayan mountains could thus be considered a present-day refugium of the Last Glacial Maximum biota [42]. Irrespective of the timeframe of these refugia, their importance for the persistence of ancient lineages cannot be underestimated.

High water availability is also linked to the persistence of forests or blocks of forests within broader ecoregions. Forests or partly forested ecoregions account for most of this ancient richness and endemism, but only one lineage, Cedrus (Pinales) has a tree habit. The other plant lineages are predominately herbs, shrubs, and geophytes (herbs), as well as one succulent and parasitic genus (Cynomorium). All lineages occur in forested ecoregions but are not strictly restricted to forests. The patchiness and heterogeneous nature of the mixed forested ecoregions (of the Mediterranean Basin) may account for the richness and endemism patterns found because of the fragmented landscape and ecotones (animal and plant lineages can occur in sclerophyllous patches or ecotones within these forested ecoregions). So, ecoregions (or vegetation units) in their entirety are perhaps not as important as the micro-habitats found within them.

Micro-habitats and micro-climates may play a very important role in the persistence of ancient lineages. The persistence of some palaeoendemic plant lineages in the higher parts of the Baetic–Rifan Range may indirectly be the result of micro-habitats being buffered by climatic variations [39]. Numerous bird and bat species depend on Mediterranean tree micro-habitats during their life cycles for food, shelter, and breeding habitat [43]. This also applies to other biota found in the Mediterranean Basin [44,45], and is particularly important for amphibian lineages that persist in moist micro-habitats [46,47].

Patch size and isolation, and their consequences for local extinctions, are also important considerations in a region as diverse (climate, geomorphology, habitats and vegetation) as the Mediterranean Basin. Patterns of local habitat occupancy and colonisation–extinction dynamics are often driven by patch isolation, the structure of the intervening matrix, and edge effects [48]. The relative importance of patch size and isolation on local extinction seems to vary in the Palearctic. In semi-natural Mediterranean mountain grasslands (NE Iberian Peninsula), the magnitude of extinction debt (i.e., the proportion of extant specialist species of the focal habitat expected to eventually become extinct as the community reaches a new equilibrium after environmental disturbance [49]) was related to the percentage of patch area reduction [50]. In calcareous grasslands and heathlands of the United Kingdom, several drivers influenced local extinction, with connectivity loss being the strongest and suitability change being moderately important. Interestingly, in some cases, changes in habitat patch size have only weak effects (e.g., [51]). In the case of large-scale rapid changes, such as glacial cycles, patch size and isolation (especially within refugia) would have played a role in the persistence of ancient lineages.

Other important factors are marine transgressions and the persistence of forest refugia. The transformation of the Paratethys Sea into the Sarmatian Sea-Lake, and its shallowing and subdivision into the Black and Caspian seas, occurred ca. 14 My ago [52]. The vegetation in the early, middle, and late Miocene shows that various forests (broad-leaved deciduous, broad-leaved evergreen, coniferous montane, mixed mesophytic, sclerophyllous subhumid) dominated the vegetation, with minor segments of intrazonal vegetation [53]. In the West Palearctic, the Messinian salinity crisis (late Miocene, starting ca. 5.96 My ago) resulted in sea levels dropping by ca. 50 m [54]. Pinus pollen features prominently in the cores of this time. There is an overrepresentation of Pinus, as well as herbs (including rare arid species such as Lygeum, Neurada, and Nitraria), at least in some areas. Furthermore, trees were less abundant and were mostly represented by Quercus species. However, overall, the pollen data indicate an arid climate and open vegetation. Taxa such as Avicennia and Taxodiaceae also suggest a subtropical climate [54]. Fluctuations in tree species support forest development during relatively humid periods and contractions during more arid periods, respectively [55]. Nevertheless, temperate and subtropical forests presumably persisted during this time, if only in the form of localised refugia, and these potentially housed ancient lineages, which is especially important for forest-associated plants. Any associated freshwater refugia would have been able to accommodate the endemic amphibian lineages through the drier periods.

On our maps (Figure 1), two desert ecoregions (Central Persian desert basins; Kopet Dag semi-desert) had relatively high richness, with the Central Persian desert basins also displaying high endemism. Noroozi et al. [56] examined the biodiversity and endemism of Iranian plants. The Irano-Turanian phytogeographical region harbours 88% of the Iranian endemics, the majority of which are restricted to the Irano-Anatolian biodiversity hotspot. The ecoregions in this hotspot are mostly the Zagros Mountains forest steppe, followed by the Eastern Anatolian montane steppe, Elburz Range forest steppe and Kopet Dag woodlands and forest steppe, and Kopet Dag semi-desert [57,58]. Additionally, ca. three-quarters of the endemic species are restricted to mountain ranges, with endemism increasing along an elevational gradient, resulting in the alpine zone harbouring a disproportionally high number of endemics [56]. This may partly explain the high ancient richness of plants and possibly animals in the Kopet Dag semi-desert.

Among the animal lineages, amphibians are likely linked to survival in sheltered environments with persistent freshwater bodies over geological time. In the case of Proteus and Speleomantes, these are actually underground environments, which allowed these lineages to survive many thousands of kilometres away from their closest relatives, likely North American taxa. In contrast, most of the reptile and rodent lineages are aridity-adapted, and their diversity peaks in moderately arid ecoregions.

The other possibility is that these ancient animal and plant lineages originated elsewhere and are recent additions to the ecoregions they currently occupy. Seen from this perspective, the patterns illustrated here are actually patterns of survival. There are additional cases where lineages have likely survived here but subsequently expanded elsewhere (e.g., the plant subfamily Fumarioideae, the core lineage of the adder subfamily Viperinae, rodent lineages such as the subfamily Gerbillinae, the genus Sicista), meaning they are currently no longer endemic. It is also possible that some lineages that were endemic to our study region have recently gone extinct through human agency. One example would be the Sardinian pika [59], although perhaps this was not old enough to meet our antiquity criterion.

Numerous Palearctic bird lineages are of recent origin (i.e., <40 My old) [60]. The lack of ancient endemic bird lineages is unusual and perhaps unique among the world’s biogeographic regions. Few bird groups differentiated within the Mediterranean Basin (e.g., Sylvia spp.). Additionally, few species evolved in Mediterranean forests dominated by sclerophyllous evergreen tree species. These results are presumably due to the history of vegetation belts and associated faunas during the Pleistocene. Many bird species invaded the Mediterranean Basin only later, and current distributions are linked to the Quaternary history of the western Palaearctic [61].

While mapping a limited number of lineages, as performed here, is less than ideal towards the delimitation of centres of endemism, it is nevertheless informative to point out where, across our study region, localised lineages are found (Figure 2). Indeed, very few lineage distributions overlap well enough to allow for describing any one area as a centre of endemism, even when narrowly distributed lineages are supplemented with lineages whose distribution can easily be described as coinciding with previously described centres of endemism, or with widespread lineages that are equivalent to single moderately homogeneous large biochoria, such as the Siberian taiga, where widespread species show limited variation [62]. This reflects the stepwise differences between the lineages’ occupancy of ecoregions from west to east, a context with insufficient pattern for identifying centres of endemism [63,64]. In the western Mediterranean, some lineages are endemic to the Iberian Peninsula, whereas others are endemic to Italy and southern France. The eastern Mediterranean, despite the high values mapped in Figure 1b (due to this area being central to the study region and, thus, adding up numerous lineages with moderately narrow ranges), has few lineages with truly narrow ranges. Iran and Central Asia have two endemic genera each and share a fifth lineage (Figure 2).

It has to be kept in mind that, where species are to be considered, the number and even location of such centres of endemism could be considerably different. This could also differ if analysing distributions for smaller units than the ecoregions [17] considered here, which are not only large but also intuitively defined. One further difficulty that could alter our results has to do with lineage age, given that different phylogenies provide different ages for the same lineage, and future phylogenetic studies using different calibration points could yield different results. Nonetheless, we view the geological ages provided in Table 1 as useful guidelines in understanding the antiquity of Palearctic lineages.

5. Conclusions

The Palearctic is the largest global biogeographical unit [65], and it houses the largest block of Mediterranean vegetation [66], which accounts for a substantial amount of the ancient richness and endemism in the western Palearctic. There are some desert outlying ecoregions that also show high ancient richness and endemism. The Palearctic represents a modestly high level of richness, endemism, and antiquity in the Old World. Additionally, it is a temperate region positioned immediately adjacent to the north of the two important tropical regions of the Old World, namely, the Afrotropical and Indo-Malaysian regions, which are older in origin and have higher levels of richness and endemism, making it an important area of continuity in the Old World but increasingly depauperate with increasing latitude (northwards) and longitude (eastwards). The conditions are too harsh for humidity-dependent eastern Palearctic lineages and also, in many cases, for western ones, requiring at least seasonal, reliable precipitation, which results in lower richness and endemism values for Central Asia.

The western part of the Palearctic has a long history of conservation (e.g., [67]), and phylogenetic measures have been recently incorporated (e.g., [15]), although regional approaches highlighting specific ancient lineages are lacking. While these lineages can potentially boost diversity indices (e.g., phylogenetic diversity [68]), the conservation value of ancient lineages is based on their uniqueness and age, and these are often compounded by rarity. Consequently, it is not only important to conserve these lineages, but they should also be used as flagship species in the study region, where their uniqueness and antiquity deserve greater recognition. Age is currently not a universal criterion for flagship species selection [69], but global approaches in this direction [70] should stimulate similar work at the regional scale. As relevant to the Palearctic specifically, molecular and paleontological data, currently only available for some of the lineages considered here, will no doubt corroborate some of our findings and challenge others.

Some of the ancient lineages in this study have adaptations to cope with aridity and may extend into the more arid, or anthropogenically transformed, parts of the eastern Palearctic. Climate change is a major global challenge, and the Palearctic will likely be affected more than most other parts of the world [71]. Despite aridity adaptations, the lineages extending into the eastern Palearctic may not cope well with other aspects linked to current anthropogenic climatic change. Ancient taxa that have survived numerous climate upheavals in the past may or may not be prepared for anthropogenic climatic change, and this should be tested under multiple modelling scenarios.